Amnesty International has said Burma's military government have detained 96 pro-democracy activists since November, when it promised to stop such arrests.
Amnesty said political detainees were being tortured and ill-treated
The human-rights group said many had been trying to gather evidence of the suppression of last year's protests, in which at least 31 people were killed.
At least 1,850 activists are currently being detained, including 700 who were arrested after the protests, it added.
On Thursday, Western leaders urged Burma to respect its citizens' rights.
In a joint appeal, foreign ministers from the US, UK and France said the need for "progress towards a transition to democracy and improved human rights in Burma" would be a priority at this years' World Economic Forum in Davos.
The ministers said the Burmese government had met none of the list of demands made in a UN Security Council resolution in October, including the release of all political prisoners.
In a report published on Friday, Amnesty International said 96 activists had been detained since Burma's prime minister assured UN Special Representative Ibrahim Gambari in November that such arrests had been halted.
"Four months on from the violent crackdown on peaceful demonstrators, rather than stop its unlawful arrests the Myanmar government has actually accelerated them," said Catherine Baber of the group's Asia-Pacific programme.
"The new arrests in December and January target people who have attempted to send evidence of the crackdown to the international community, clearly showing that the government's chief priority is to silence its citizens who would hold them to account."
Amnesty said at least 15 protesters and their supports had been sentenced to prison terms since November, and that it had received reports that detainees were being tortured.
More than 80 people remain unaccounted for since then and "are likely the victims of enforced disappearance", it added.
Among those arrested recently is the well-known poet, Saw Wai, who was detained after one of his love poems was found to contain a hidden message criticising Burma's military leader.